The present invention is related to converting lighter hydrocarbons to heavier hydrocarbons and more specifically to cleaning water produced while converting the lighter hydrocarbons, disposing of undesired contaminants from the associated conversion process, and providing additional power for the conversion process and other uses including supplying additional compressed air for use in the conversion process.
Synthesis gas, or xe2x80x9csyngas,xe2x80x9d is a mixture of gases prepared as feedstock for a chemical reaction. It is primarily a mixture of carbon monoxide and hydrogen that may be used to make hydrocarbons or organic chemicals. Syngas may be produced for use as part of a Fischer-Tropsch process to convert lighter hydrocarbons (e.g., natural gas) to heavier hydrocarbons (Cst).
The synthesis production of hydrocarbons by the catalytic reaction of carbon monoxide and hydrogen is well known and generally referred to as the Fischer-Tropsch process or reaction. Numerous catalysts have been used in carrying out the process. The Fischer-Tropsch reaction is very exothermic and temperature sensitive whereby temperature control is required to maintain a desired hydrocarbon product selectivity. The Fischer-Tropsch reaction can be characterized by the following general reaction: 
Water produced by the Fischer-Tropsch reaction is often contaminated with alcohol and other hydrocarbons. In addition, water produced during synthesis gas production may also contain contaminants. Therefore, the contaminated water should generally be cleaned prior to disposal or prior to any use for other purposes.
In the past a number of techniques have been used to dispose of contaminated water from Fischer-Tropsch processes. A water treatment facility typically has been necessary. Such a facility might use biological treatments, which are fairly capital intensive. An approach using a stripper has been suggested in U.S. Pat. No. 5,053,581, entitled xe2x80x9cProcess For Recycling And Purifying Condensate From A Hydrocarbon Or Alcohol Synthesis Process.xe2x80x9d
Two basic methods have been employed to produce synthesis gas used as a feedstock in Fischer-Tropsch reactions. The two methods are steam reforming, wherein one or more light hydrocarbons such as methane are reacted with steam over a catalyst to form the desired synthesis gas of carbon monoxide and hydrogen, and partial oxidation, wherein one or more light hydrocarbons are combusted or reacted sub-stoichiometrically to produce the desired synthesis gas.
The basic steam reforming reaction of methane is represented by the following formula: 
The steam reforming reaction is endothermic and a catalyst containing nickel is often used. The hydrogen to carbon monoxide ratio of the synthesis gas produced by steam reforming of methane is approximately 3:1.
Partial oxidation is the non-catalytic, sub-stoichiometric combustion of light hydrocarbons such as methane to produce the desired synthesis gas. The basic reaction is represented by the following formula:
CH4+xc2xdO2xe2x86x92CO+2H2 
The partial oxidation reaction is typically carried out using high purity oxygen which can be quite expensive. The hydrogen to carbon monoxide ratio of synthesis gas produced by the partial oxidation of methane is approximately 2:1.
In some situations the two basic methods may be combined. The combination of partial oxidation and steam reforming, known as autothermal reforming, wherein air may be used as a source of oxygen for the partial oxidation reaction has satisfactorily been used to produce synthesis gas. For example, U.S. Pat. Nos. 2,552,308 and 2,686,195 disclose low pressure hydrocarbon synthesis processes wherein autothermal reforming with air is used to produce synthesis gas for an associated Fischer-Tropsch reaction. One benefit of autothermal reforming is using exothermic heat from the partial oxidation reaction to supply necessary heat for the associated endothermic steam reforming reaction.
In accordance with teachings of the present invention, a system and method are provided for treatment and disposal of undesired products and/or contaminants produced by a Fischer-Tropsch process while converting lighter hydrocarbons to heavier hydrocarbons. Teachings of the present invention result in more efficient cleaning of water produced by the Fischer-Tropsch process. One or more gas turbines are preferably included for use in disposing of contaminants and/or other undesired products produced by the Fischer-Tropsch process. The gas turbine or turbines are preferably designed to accommodate supplying steam and/or heavily moisture laden air to an associated combustion chamber and gas expansion section.
One aspect of the present invention includes a system having one or more gas turbines, an autothermal reformer for producing synthesis gas, a synthesis gas water wash column, a Fischer-Tropsch reactor and a water stripping column. Water produced by the Fischer-Tropsch process is preferably separated from other Fischer-Tropsch products and directed to the synthesis gas water wash column to remove undesired contaminants from synthesis gas prior to entering the Fischer-Tropsch reactor. Contaminated water from the synthesis gas water wash column is preferably directed to the water stripping column. Suitable fluids such as steam and/or tail gas are preferably supplied to the water stripping column for use in removing gases, soluble compounds, and other undesired contaminants from the contaminated water. A stream of contaminated steam is preferably directed from the water stripping column to a combustion chamber of at least one of the gas turbines. The stripped water is preferably directed to a disposal facility and/or may be recycled for use in the synthesis gas water wash column.
Another aspect of the present invention includes providing systems and methods for treatment and disposal of undesired products and/or contaminants produced by any process which converts a synthesis gas to a desired product or products. Teachings of the present invention may be used with other conversion processes associated with a methanol reactor, dimethyl ether (DME), an ammonia reactor or any other reactor which converts a synthesis gas to a desired product or products.